1. Field of the Invention
The present invention relates to a conductive composition, a conductive member, a conductive member production method, a touch panel, and a solar cell.
2. Description of the Related Art
In recent years, as an input device, a touch panel has been mounted on display devices such as a liquid crystal panel and electronic paper. The touch panel is known to be constituted by various systems such as a resistive film system, a surface acoustic wave system, and a capacitive system. Among these, the capacitive system is known as a system that facilitates multipoint touch and makes it easy to produce a large-area touch panel. For example, there is a disclosure regarding a capacitive touch panel using indium tin oxide (ITO) as a transparent conductive material.
However, indium as a raw material of ITO is expensive, and stable supply thereof is limited. Moreover, in order to be made into a thin film, indium requires a vacuum process, and accordingly, the production cost increases. Furthermore, the ITO film has problems in that it is brittle and exhibits poor bending resistance. Therefore, alternative substances such as a metal nanowire, a carbon nanotube, PEDOT, and polyaniline are being suggested.
For example, a conductive member having a conductive layer containing conductive fiber, such as a metal nanowire, a carbon nanotube, and a complex consisting of a carbon nanotube and a metal, has been suggested (for example, see JP2009-505358A). In the conductive member, a conductive layer containing plural metal nanowires is placed on a substrate, and the conductive layer contains a photocurable composition as a matrix. Accordingly, by being subjected to pattern exposure and then development, the conductive member can be easily processed into a conductive member having a conductive layer including an intended conductive region and a non-conductive region.
As another system of the conductive fiber-containing conductive member, it is possible to use a method in which a non-photocurable composition as a matrix is added to a conductive layer, the resultant is dried and/or crosslinked if necessary by a condensation reaction or a polymerization reaction to form a conductive layer, a resist layer is then formed image-wise on the conductive layer by using an etching resist or the like, and then an etching step is performed; a method in which a conductive network in a uniformly formed transparent conductive layer is irradiated with laser beams such that a portion of the network is cut; or the like. By such a method, the conductive member can be easily processed into a conductive member having a conductive layer including an intended conductive region and a non-conductive region (for example, see JP2010-507199A and JP2010-44968A).
Moreover, as another system of the conductive fiber-containing conductive member, a conductive layer transfer-type conductive layer formed in a manner in which a conductive fiber-containing conductive member is formed on a temporary support, transferred to a glass substrate or the like, and subjected to patterning if necessary by a method such as photolithography has been suggested (for example, see JP2006-35771A and JP2009-251186A).
As the conductive fiber preferably used for the conductive member, various materials including a nanowire and a nanorod of metals such as silver, gold, and copper, a carbon nanotube, a carbon nanorod, and a complex of a carbon nanotube and a metal are known. Among these, conductive metal fiber formed of metals such as silver, gold, and copper is known to more preferably form an excellent conductive member having low resistance and a high degree of optical transparency. Particularly, a silver nanowire excellent in the balance among low resistance, durability, and cost is preferably used.
However, when these conductive members using the conductive metal fiber are exposed to harsh conditions such as a high temperature, a high humidity, and the presence of ozone for a long time, increase in resistivity, which is assumed to result from oxidation or deformation of metal, occurs in some cases. Therefore, depending on the purpose, the conductive members are required to be improved in terms of weather resistance in some cases.
As a method for improving weather resistance of a conductive metal fiber-containing transparent conductive material, a method of using a metal-adsorbent compound having a specific structure is known (for example, see JP2009-505358A and JP2009-146678A). This method is effective when the compound is stored under specific conditions. However, since the metal-adsorbent compound exhibits strong absorptivity with respect to the conductive metal fiber, the conductive metal fibers are aggregated during the production of the transparent conductive material, and homogeneity of the conductive layer deteriorates. Consequentially, conductivity or transparency of the conductive layer deteriorates, or contact resistance between the conductive metal fibers increases, and this leads to a problem in that conductivity of the conductive layer deteriorates in some cases.
As a method for producing an aqueous dispersion containing metal nanowires, a method of adding a metal complex solution or metal ion solution to an aqueous solvent containing a halogen compound and a reductant is known (for example, see JP2010-84173A). In the production method, in order to improve purity of the metal nanowires, desalting treatment is preferably performed. Presumably, when the desalting (washing) treatment described in examples of JP2010-84173A is performed, most of the reductant that does not make contribution to formation of the metal nanowires may be removed. In JP2010-84173A, neither a method of intentionally leaving a reductant added for reducing a metal complex nor an effect of such a method is described.
As described above, it cannot be mentioned that the conductivity of the conductive metal fiber-containing transparent conductive material is stably kept to a sufficient degree by the technique in the related art even under harsh conditions such as a high temperature, irradiation of actinic radiation, or the presence of ozone. Therefore, improvement of weather resistance thereof is required.